Valve lifters are used in internal combustion engines to convert rotational motion of an engine cam into linear motion, for controlling the position of gas exchange valves. A typical design includes a lifter body coupled with a pushrod configured to actuate a rocker arm of one or more gas exchange valves. The lifter body includes a roller positioned in contact with the engine cam, such that rotation of the engine cam causes the valve lifter to slide within a lifter bore formed in the engine housing. Sliding of the valve lifter adjusts the pushrod, which in turn moves the rocker arm in a well-known manner.
The roller may be generally cylindrical and contacts an outer surface of the cam, such that a desired interface between the roller and the cam outer surface is essentially linear. During service in the engine, valve lifters may become misaligned with the cam via rotation of the valve lifter within the lifter bore. The causes of such misalignment appear to vary from engine to engine. Even seemingly identical engine designs can exhibit different misalignment issues of their valve lifters over the course of the engine's service life. Adding to the complexity, some valve lifters tend to rotate more, or differently than other valve lifters even within the same engine.
Various strategies have been proposed over the years to limit valve lifter rotation. One technique employs a guide mechanism coupled with the valve lifter. U.S. Pat. No. 3,886,808 to Weber teaches such a design. In Weber, the guide mechanism includes a vertically disposed leg which seats in a slot formed on the valve lifter, and a pair of cylindrically shaped arms which seat in a circumferential groove also formed on the valve lifter. A hook connected to the leg seats in a bore in a cylinder block of the engine, apparently preventing the guide and valve lifter from rotation.
Variations on the basic guide design taught by Weber have been developed over the years. As engine designs, duty cycles, and performance characteristics change with continued progress of the art, however, both the nature and extent of valve lifter rotation and its consequences in an engine can change as well. Certain strategies for limiting or otherwise controlling valve lifter rotation that may have been satisfactory in the past have become unsuitable. As is the case with many engineering solutions, such strategies may also have been imperfect to begin with. Failure or damage of a valve lifter and related components can necessitate costly servicing or repair, and shorten the service life of the engine. The poorly understood causes of valve lifter rotation coupled with the desire to avoid redesigning an engine, thus render the pursuit of solutions in this technical area complex and unpredictable.